The present invention relates to optical communication systems, and more particular, to a bandwidth variable wavelength router.
A wavelength router has applications in wavelength division multiplexed (WDM) optical networking environments. Prior designs for wavelength routers based upon polarization based techniques are often difficult to manufacture, provide static spectral processing, and are not effective in multi-bit-rate networking environments.
In one embodiment of the present invention, an optical device comprises a plurality of birefringent waveplates and a plurality of polarization rotators. The birefringent waveplates are oriented at a substantially common angle about an optical axis. The polarization rotators are arranged among the plurality of birefringent waveplates such that a wavelength division multiplexed optical signal propagating through the polarization rotators and the birefringent waveplates is processed into a first subset of wavelengths comprising substantially a first polarization and a second subset of wavelengths comprising substantially a second polarization.
In another embodiment of the present invention, an optical device comprises a first birefringent crystal having a first length, a second birefringent crystal having a second length, and a dynamic polarization rotator. An optical signal propagating through the first and second birefringent crystals has an effective optical path length based, at least in part, upon the first length of the first birefringent crystal and the second length of the second birefringent crystal. The dynamic polarization rotator adjusts the effective optical path length of the optical signal in response to a control signal.
In yet another embodiment of the present invention, an optical device comprises a plurality of birefringent waveplates and a plurality of polarization rotators. The polarization rotators are arranged among the plurality of birefringent waveplates such that an optical signal propagating through the polarization rotators and the birefringent waveplates is processed into a first subset of wavelengths comprising substantially a first polarization and a second subset of wavelengths comprising substantially a second polarization. At least one of the plurality of polarization rotators is operable to change the polarization state of beam components associated with the optical signal.
Some, none, or all of the embodiments described herein may embody some, none, or all of the advantages described herein. Manufacturing birefringent crystals or waveplates having unique angles, as with prior art wavelength routers, is a delicate process. An advantage provided by at least one embodiment of the present invention is that the birefringent waveplates are all arranged at a substantially common angle, (e.g., approximately zero degrees) with respect to a reference optical axis. In this respect, the cost and complexity associated with manufacturing and arranging the birefringent waveplates is reduced. For example, a designer is free to choose any common angle for all of the birefringent waveplates. As a result, angles near vulnerable cleavage planes, which induce chipping or cracking, can be readily avoided. Damage and waste are further reduced through efficient raw material utilization. For example, because all birefringent crystals are cut at a substantially common angle, an angle can be selected which results in the best yield.
Not only do the principles of the present invention advantageously reduce complexity and enhance flexibility of design and fabrication as described above, they facilitate a compact single piece waveplate implementation of a wavelength router. For example, because the birefringent waveplates may be oriented at a substantially common angle, it becomes possible to replace multiple longitudinally aligned individual birefringent waveplates with fewer waveplates arranged with the polarization rotators in a compact assembly that uses an optical beam path that is folded. In one embodiment, the multiple birefringent waveplates may be replaced by a single birefringent waveplate oriented at an angle. The compact size of the wavelength router results in higher optical device densities and a robust operation.
In a particular embodiment of the present invention, the spectral bandwidth of the wavelength channels associated with output signals is made variable in response to control signals applied to portions of the birefringent waveplates. By implementing the birefringent waveplates using a dynamic polarization rotator positioned between birefringent crystals, the effective optical path length propagating through the birefringent waveplate can be increased or decreased. By increasing the optical path length of an optical signal, the bandwidth of each wavelength channel associated with the output signals is narrowed. By decreasing the optical path length of an optical signal, the bandwidth of each wavelength channel associated with the output signals is widened. As a result, the use of a dynamic polarization rotator to control the effective path length of an optical signal facilitates variable bandwidth wavelength routing.
In another embodiment of the present invention, dynamic polarization rotators may be operated by the application of control signals to produce a switchable wavelength router. A technical advantage of a switchable wavelength router is that it provides a switchable beam path control in optical network applications. This allows the switchable wavelength router to function as an optical wavelength router in an optical network and to perform, for example, protection switching and restoration of optical data paths. Additionally, it can recognize new wavelength bands and switch subsets of wavelength channels among outputs.
Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, description and claims.